Recording tape is a known medium for the storage of audio, video, and computer data. In the field of computer data recording (that is, the writing, or storing, of analog or digital data onto tape and the reading, or retrieving, of written data from tape), perhaps the most important feature of tape transport and recording equipment design is the interface between the tape and recording head interface. At the interface, well-controlled, intimate contact between the head and tape is essential to achieve high quality recording performance. Critical to this contact is smooth, clean, consistently tensioned and aligned tape over the full range of tape operating motion. Mechanical misalignments, tape deformation, and foreign debris degrade the interface quality and reduce performance.
Tape cartridges (generally defined as having one internal spool of tape) and cassettes (generally defined as having a tape supply spool and take-up spool internal to the device) provide for physical protection of the recording medium--typically magnetic tape--during storage, handling, and operations in the recording equipment. Cartridges and cassettes provide for a much improved protection over earlier open reel tape carrier designs. Cassettes typically include some form of internal tape guiding mechanism.
There are many commercial magnetic tape recording cartridges and cassettes, using tapes of various cross-width dimensions (for example, 4 mm, 1/4-inch, 8 mm, 1/2-inch, and 19 mm), currently used for storage and retrieval of digital data. Since its introduction in the 1950's, half-inch magnetic tape has been particularly a vital part of data processing. In current technology, a magnetic tape cartridge using half-inch magnetic tape for storing digital data is defined in American National Standard Institute's (ANSI) proposed standard X3-180-1990. This cartridge (popularly known as the "3480/3490" cartridge) contains a single reel of magnetic tape, including a leader block for interfacing with an automated threading subsystem of an adapted tape drive (referred to hereafter as the "leader block tape cartridge"). This leader block tape cartridge is fuller illustrated and described in U.S. Pat. No. 4,383,660, and 4,452,406. Tape transport drives using the leader block tape cartridge require a mechanism for extracting the leader block, threading the tape around a tape recording path and into a take-up reel in the drive, and, in reversing this process, to re-insert the leader block back into the cartridge after rewinding. This "loading mechanism" adds, size, complexity, cost and undesirable latencies to the tape transport. Further, the transport must contain a take-up reel and all of the necessary tape guiding and alignment features to support a stable, effective tape-head interface. In addition, the mechanism must meet the requirement of handling the tape gently yet rapidly; tape handling is a limiting performance factor. In general, type of cartridge and transport combination has the disadvantage of requiring a relatively long, external tape path to accommodate the required tape guiding and alignment features and the take-up reel. Moreover, the tape must always be fully rewound back into the cartridge before the cartridge can be removed from the transport. The complexity of such mechanisms is demonstrated, for example, in U.S. Pat. Nos. 4,334,656 and 4,335,858. Tape guide devices for leader block cartridge use are also complex; see e.g., U.S. Pat. No. 5,218,501 (Sellke). Similarly, mechanisms for re-insertion of the leader block are also complicated; see e.g., U.S. Pat. No. 4,949,914 (itself citing to many other patents in the field).
Technical advances have brought about thinner and stronger tape substrates that greatly increase the quantity of tape that can be contained in any given cartridge or cassette. Advanced recording strata on these substrates allow for much smaller recorded data bits. These enhanced recording densities are supported by advanced read and write head mechanisms that support higher track densities as well. The effective application of all these technical advances requires improved tape-to-head interface and tape handling by the transport.
Therefore, there is a need for a magnetic tape cassette which takes advantage of improvements in magnetic tape and read-write head technology and at the same time minimizes the need for drive mounted tape guiding elements, long tape paths, and a separate take-up reel and loader mechanism.
For many years both disk drives and tape drives have been manufactured according to a de facto size standard which requires that they fit within a physical envelope measuring 31/4 inches in height by 53/4 inches in width by 8 inches in depth, known in the industry as the 51/4 inch, half-height, form factor. In addition, cassette and cartridge handling systems have been developed so that libraries with automated tape handling have become a successful reality. Therefore, there is a need for a magnetic tape cassette that is compatible with industry standard form factors and automated tape handling systems.